The distribution feeder design dictates how distribution feeder lines are laid out and interconnected to provide service to customers and there are several options. The simplest design is radial feed, which consists of a single line. This means that when any disturbances occur causing a portion of the line to be taken out of service, all customers downstream experience an outage. A common distribution feed used to add reliability, especially in commercial and industrial areas, is called a loop feed.
A loop feed serves customers off a loop that is connected to the primary feed at two ends. Electricity is directed in one direction through use of switches. When a clearance is required to do maintenance, or when a fault occurs, switches can be opened and closed to redirect the flow in an alternate direction thus serving customers along an alternate path. This design costs more than a radial system since duplicative equipment is required, but it also provides the capability of isolating faults within the loop and continuing to feed all customers except those on the section with the fault. However, if the loop feed is connected to only one substation, the whole loop will be out of service if that substation fails. The reliability of loop feeds can be enhanced by adding additional primary distribution feeds to the circuit.